PVDF reinforced with core–shell structured Mo@MoO3 fillers: effects of semi-conductor MoO3 interlayer on dielectric properties of composites

An insulating interlayer between polymer and conductive particles is crucial for suppressing the dissipation factors (tanδ) of composites. In order to restrain the large tanδ of molybdenum (Mo) particles/poly(vinylidene fluoride) (PVDF) composites while still holding a high dielectric permittivity (εr) close to the filler’ percolation threshold (fc), Mo particles were first encapsulated with a layer of molybdenum trioxide (MoO3) shell through a facile direct thermal oxidation method at 600 °C, and then were compounded into PVDF. The influences of the MoO3 coating on dielectric properties of the Mo/PVDF composites were investigated in terms of filler loading, the shell thickness and frequency. The results suggest that both the calcination time and the filler loading remarkably affect the dielectric properties of the composites. The Mo@MoO3/PVDF composites exhibit high εr but much low tanδ compared with raw Mo/PVDF because the semi-conductor MoO3 shell effectively prevents the raw Mo particles from connecting with each other thereby leading to enormously suppressed loss and leakage current even at high filler loadings > fc. With further increasing the interlayer thickness both the dielectric loss and conductivity decline accordingly thanks to the gradually pronounced suppression effect. The resulting Mo@MoO3/PVDF composites possessing the high εr but low tanδ could be the ideal dielectric materials for potential applications in microelectronics and electrical industry.